[Asterisk-Users] TDM400P vs SIP3000 x2

[Rich Adamson]

> I just got through trying to set up a Sipura 3000 and am still looking
> for answers.  There is a low volume problem (caller is underwater)  on
> the FXO port that I wish someone would have told me about and I would
> have gone the other route.  (even after upgrading firmware and
> adjusting gain settings)  More details here.
> 
> http://voxilla.com/index.php?name=PNphpBB2&file=viewtopic&t=3500&highlight=vol+volume
> http://voxilla.com/index.php?name=PNphpBB2&file=viewtopic&t=1249&highlight=vol+volume
> 
> Maybe they work great and this one is defective, but others appear to
> have a simular problem and this was my experience.

The good thing about the spa3k is it provides a substantial amount of
flexibility, and the bad thing is the flexibility (and options) make
it very difficult to configure without some fairly extensive experience
or knowledge.

I have one configured for pstn ring-thru to the fxs, but have both the
fxs port and the fxo port also registered with asterisk. (Eg, asterisk
can be totally down and pstn calls still ring thru, and my spouce didn't
need any remedial training to use the house phones lurking on the fxs
port.) With this config, the dialplan in the spa is set so that any
call starting with an "8" is routed to asterisk while all others are
sent out the pstn/fxo port. Love it.

With that config, under the Regional tab, I have fxs input=3 and
fxs output at 0. Then, on the PSTN tab, I have STA to PSTN at -2.0 and
PSTN to STA at -2.0. The end result is that non-technical fxs users
can't tell they are talking through the spa3k. (The audio levels are
just a little lower then if the spa3k wasn't in use.)

In addition, any incoming voip calls (via asterisk) ring the fxs port
with distinctive ringing, so we know from the ring where the call is
originating from. Audio via this path is no problem and depends solely
on the settings under the Regional tab.

If I want to place a call from Asterisk to the pstn thru the fxo port,
I can. The gain settings under the PSTN Line tab impact that call.
Those settings are 100% "dependent" on how far you are located from
the pstn central office, so copying other's settings will do you no
good whatsoever. We happen to be about 15,000 feet from our central
office and the measured cable loss is about -7db. In theory, I should 
be able to set the PSTN Line gains around 5.0 db (or about -2 db less 
then the cable loss), however if I do that echo is noticable. So, I 
had to back those values down -1.0 db at a time to find a value that
was an acceptable level and no noticable echo. (Since at least some
of the options within the spa3k require a reboot to take effect, I
simply rebooted the spa3k after making every change. At least that way,
I know for an absolute fact what values are actually being used
regardless of what has changed.)

There are also a couple of other settings on the spa3k that might be
impacting your quality. Obviously the port impedence needs to match
whatever your country standards are (600 ohms in the US), and I'd
make absolutely sure that is set before dicking with anything else.
On the SIP tab, look at the RTP Packet Size and ensure it says .020
(or 20 milliseconds). For whatever reason, my spa3k had a value of
.030 (30 milliseconds) and audio was not very good. I'm not sure if
that value was the default or if it somehow changed since the box
has had about five different firmware versions in it over the last
year or so. (Note: there was some discussion on the voxilla list about 
that as others were having audio quality issues as well.)

Last, on the Line 1 tab, be sure Silence Supp Enable = no, Preferred
Codec is g711u, and Symmetric RTP = yes. (Do the same on the PSTN tab.)

Given my 20+ years working for a telephone company in an engineer
role, I even find it difficult to configure the spa due to the number
of options and rather poor documentation on the majority of those
options. But, I'm fairly comfortable the spa _can_ be configured to
provide a very reasonable service in most cases. It does for us.

I have detected the spa3k will sometimes inject a little short-duration
noise and I'm pretty sure that certain voices are causing it, but I've
not spent the time to diagnose that as yet. Doesn't happen often enough
to warrant spending much time on it.

I also have a TDM04b card in the asterisk system with four pstn lines
attached to it. The quality of the audio and the functionality of both
are roughly the same. Setting the proper gains on the TDM card is no
easier or harder then setting the spa; both require an understanding
of the telco standards and playing with levels to find an acceptable
balance between levels and echo.

Rich